Glue the skins together.

Sand smooth.

Spray hairspray on the glue side of the sheeting to seal the wood. It will not get absorbed into the wood this way and you will save weight.

I'd use finishing resin. I'd apply it to the skins mixed in a large syringe in 1 inch squares (I don't want it to spread more than 1/4" in width once the sheeting is set with weight.
Line joining areas with glue.
No, the entire surface will not be spread with glue.


Finishing resin gives you more time to work.

You could cut out lattice work in the foam core, but the foam is VERY light and not as much weight savings by cutting the foam as when you use this glue method.

Brian